Photochemical particulate formation in sulfur dioxide-air mixtures

Experiments were performed studying the formation of particulates in sulfur dioxide-air mixtures irradiated by ultraviolet light. Measurements were made for five different initial sulfur dioxide concentrations (0.2, 0.3, 0.5, 0.7 and 1 ppm) and for four relative humidities (25, 50, 75 and 100%). The data show that the maximum number of nuclei (particles smaller than 0.1 μm) produced in the mixture is proportional to the initial sulfur dioxide concentration and to the square of the relative humidity. Particles larger than 0.3 μm were not present in measurable amounts in the mixture.